Glossary Plant Breeding

Positive Control. Regulation mediated by a protein that is required for the activation of a
transcription unit. Expression of the gene requires activating signal.
Potential Variability. A kind of bound variability that is released slowly in subsequent
generations when it gets converted into free variability following segregation. In most
cases, it occurs in the heterozygotes. However, if two or more genes affect the same
trait in completely additive manner, potential variability will occur in AaBb, AAbb
and aaBB. The latter two genotypes contain homozygotic potential variability that is
released very slowly because it is first converted into heterozygotic potential
variability by crossing and then converted into free variability.
Primary Structure. The sequence of amino acids in the polypeptide chain.
Primase. An enzyme that makes RNA primers during DNA replication.
Primer. A short single-stranded RNA or DNA that can act as a start site for 3’ chain
growth when bound to a single-stranded template.
Primer Walking. The use of a primer based on a sequenced area of a genome to
sequence into a flanking unsequenced area.
Prepotency. The capacity of a parent to impress its characteristics on its offspring so
they are more alike than usual. Differences in prepotency depend on homozygosity,
dominance, epistasis, and linkage. A homozygote dominant at all loci would excel in
prepotency because its close relatives would be unusually alike. Such an individual
produces only one kind of gamete; therefore, upon selfing or crossing inter se of
individuals with the same genotype will produce individuals of the same kind, that is,
genetic correlations among relatives will be very high. Multiple heterozygotes, which
produce many kinds of gametes (and hence, many kinds of individuals upon selfing),
are generally not highly prepotent.
Pre-Breeding. The sum total of all the activities related to germplasm enhancement for
future use in varietal development.
Precision Agriculture. Agriculture that makes an effective use of information
technology through data available on soil, water, environment and other related
variables.
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